The present invention relates, in general, to the connection of an originating network node to a network switch via a line appearance and, more particularly, to the determination of answer supervision at the line appearance by the originating network node.
In many instances, far party answer supervision cannot be passed backwards through the telephone network to an originating network node which is connected to a line appearance of a network switch. Unfortunately, some recent applications require answer supervision to the originating network node for proper operation. Accordingly, there is a need for a method for an originating node which is connected to a line appearance of a network switch to determine answer supervision from signaling which is present at the line appearance. Preferably, this method would be simple to implement and reliable in determining answer supervision.
This need is met by the invention of the present application wherein audible ring, which is provided to all line appearances, is detected and used to determine whether or not a far end party has answered, i.e., answer supervision, for equipment connected to the line appearance which requires answer supervision for proper operation.
In accordance with one aspect of the present invention, a method of determining answer supervision at a line appearance of a public switch telephone network comprises monitoring the line appearance to detect ringing tone received at the line appearance and timing for a first period of time from call origination. If ringing tone is not detected at the line appearance within the first period of time, receipt of answer supervision is indicated. If ringing tone is detected at the line appearance within the first period of time, the timing for the first period of time is canceled and timing for a second period of time is started from the cancellation of timing for the first time period. The timing for the second period of time is restarted each time ringing tone is detected at the line appearance during the second period of time with receipt of answer supervision being indicated if ringing tone is not detected within the second period of time.
Timing for the first period of time preferably comprises timing for a period of time substantially equal to ringing tone cycle time plus post dial delay time for the public switch telephone network. Timing for the second period of time preferably comprises timing for a period of time substantially equal to ringing tone cycle time.
In accordance with another aspect of the present invention, a method of determining answer supervision at a line appearance of a public switch telephone network comprises monitoring the line appearance for receipt of ringing tone, indicating receipt of answer supervision if ringing tone is not received, and indicating receipt of answer supervision if ringing tone is initially received and is terminated.
Indicating receipt of answer supervision if ringing tone is not received preferably comprises indicating receipt of answer supervision if ringing tone is not received within a first period of time substantially equal to ringing tone cycle time plus post dial delay time for the public switch telephone network. Indicating receipt of answer supervision if ringing tone is initially received and is terminated preferably comprises timing for a second period of time substantially equal to ringing tone cycle time, restarting the timing for a second period of time each time ringing tone is detected within the second period of time, and indicating receipt of answer supervision upon expiration of the second period of time.
In accordance with yet another aspect of the present invention, apparatus for determining answer supervision at a line appearance of a public switch telephone network comprises a ringing detector coupled to the line appearance to detect ringing tone received at the line appearance. A first timer times a first period of time from call origination with receipt of answer supervision being indicated if ringing tone is not detected at the line appearance within the first period of time and the timing for a first period of time is cancelled if ringing tone is detected at the line appearance within the first period of time. A second timer times for a second period of time from cancellation of the timing for the first time period, the second timer being restarted for the second period of time if ringing tone is detected at the line appearance during the second period of time. Receipt of answer supervision is indicated if ringing tone is not detected within the second period of time.
In accordance with still another aspect of the present invention, apparatus for determining answer supervision at a line appearance of a public switch telephone network comprises a ringing detector coupled to the line appearance to detect ringing tone received at the line appearance. Receipt of answer supervision is indicated if ringing tone is not received, and receipt of answer supervision is indicated if ringing tone is initially received and is terminated.
In accordance with an additional aspect of the present invention, apparatus for determining answer supervision at a line appearance of a public switch telephone network comprises a switch and a ringing detector coupled to the line appearance to detect ringing tone received at the line appearance. The switch is programmed to indicate receipt of answer supervision if ringing tone is not received, and if ringing tone is initially received and is terminated.